This invention relates to liquid diluting and transfer valve systems, and more particularly to controlling the environment in which frictional valve faces, which do not maintain a mechanically perfect seal and rely somewhat on a filled capillary in operation, are operated in a controlled environment to inhibit breakdown caused by the imperfect seal.
Liquid transfer systems utilizing mechanically operated liquid transfer valves are useful in medicine, biology, chemistry and the like fields, in research and routine testing which is required to produce fluid mixtures of specific concentrations, accurately and automatically, and can feed known quantities of such fluids to selected locations. Such liquid transfer valve assemblies generally comprise a central element and one or more outer elements engaged against opposite faces of the central element to sandwich the central element therebetween. The central element is slidably movable with respect to the other elements between first and second positions. Measuring conduits are formed in or on one of the element and at least a pair of ports are provided in adjacent elements. Each of the ports, in one element, aligns with the port carried by the other element so that two fluid paths are defined. The central member is indexed to a first position to align one measuring conduit with one of the fluid paths for reception in that one conduit of a portion of the liquid sample. The central element is then moved to a second position and by virtue of such movement the volume of the sample in the measuring conduit is segmented and deposited in the other fluid path for combining with a diluent introduced therein so as to provide a precise dilution and, accordingly, a specific concentration of one sample.
The transfer valve assembly includes movable elements which move linearly or are rotated or both to effect the segmenting of the precise volume quantities of a sample. By providing a second conduit associated with the central member, a predetermined volume of diluent may be provided to effect a second dilution. In blood sampling, for example, the first dilution may be utilized for the purpose of making a white blood cell evaluation while a second dilution can be utilized to evaluate the red blood cell which requires substantially more dilution. The problem with these slidable frictionally engaged surfaces of the various elements of the transfer valve assemblies is that they do not form a perfect seal therebetween and are constantly being moved relative to each other causing seepage which results in a molecular layer of liquid between the sealing surfaces due to internal pressure or which layer is drawn by capillary action between the sealing surfaces as a result of surface finish porosity in the mating halves or imperfection in the flatness of the mating halves. As the volatile contents of these fluids, which are being transferred, evaporate along the interface or junction of the sealing surfaces or even more predominant on the sliding valve at the intermittently exposed ends, a residue of non-volatile solid remains forming abrasives and/or sludge. This residue results in a degradation or minute lifting of the sealing members. Either or both phenomena can contribute to increasing the flow, evaporation, residue cycle resulting in excessive outward leaking of captured fluids or inward leaking of the external environment when negative pressures are applied to the valve members. The buildup of solids at the junctions of the conduits or ports of the various elements can result in the failure of the valve assembly and at the very least requires the dismantling and removal of any evaporated residue forming on the faces of the sealing surfaces, particularly at the junctions of the ports and conduit areas.
In U.S. Pat. No. 4,702,889 a transfer valve assembly uses disk-like valve elements having frictionally engaged faces with passageways for passing both sample liquid and rinse liquid along with a continuous groove formed in one of the respective faces. The continuous groove is provided for treating the aforesaid problem by isolating the passageway openings to the faces for blocking passage of liquid material along the face to the periphery of the engaged face. Of course, the problem is that it does not stop the seepage and merely collects the seepage which still can evaporate and ultimately overflow the groove which is meant to contain it and of course must be periodically cleaned.
Whether the valve elements are pivoted, slidable or rotatable, the same problem exists and that is seepage of material between the frictionally engageable surfaces which evaporates and causes a buildup between the sealing faces of the valve elements. The present invention is directed to eliminate evaporation of such seepage and prevent a solid buildup between the faces tending to separate them more and to cause additional continuous and greater progressive buildups.